Mad cow disease was first reported in the United Kingdom in 1986, peaking in 1993 with almost 1,000 new cases per week.

In 1996, variant Creutzfeldt-Jakob Disease (vCJD) was detected in humans and linked to the mad cow epidemic. Eating contaminated meat and cattle products is presumed to be the cause.

Both are fatal brain diseases with unusually long incubation periods, often lasting years.

To date, no case of mad cow disease has been identified in the United States.

As of April 2, 2002, a total of 125 cases of vCJD had been reported in the world: 117 from the United Kingdom, six from France, and one each from Ireland and Italy.Source: CDC

EDMONTON, Alberta (CNN) --Mexico, Japan and South Korea on Wednesday joined the United States in temporarily banning Canadian beef after health officials announced Tuesday that a cow slaughtered in northern Alberta tested positive for mad cow disease.

In the country's first case in a decade, an 8-year-old cow was tested and killed in January after showing signs of illness, Canadian agriculture officials said. Tests in England confirmed signs Tuesday of Bovine Spongiform Encephalopathy (BSE), or mad cow disease.

The fatal brain-wasting disease is believed to be spread through contaminated cattle food and cannot be passed from cow to cow. A human disease -- variant Creutzfeldt-Jakob Disease (vCJD) -- was first identified in 1996 and linked to eating mad cow-contaminated meat and cattle products.

Health officials said they think they have limited the spread of the disease. They have identified two more herds that might have been linked to the cow, said Dr. Claude Levigne of the Canadian Food Inspection Agency. Those herds have been placed under quarantine, along with the original herd where the cow was first discovered.

According to Levigne, those cows will be killed and brain samples will be tested for BSE, with results in at least three days.

Canada is the world's fourth largest exporter of beef, with the United States its largest customer, according to the National Cattlemen's Association. Although the United States imports 12 percent of Canada's beef cattle, only 7 percent of the beef in U.S. grocery stores is from Canada. The largest amount of imported beef comes from Australia, followed by New Zealand and then Canada.

U.S. Agriculture Secretary Ann Veneman said she is confident of the safety of the U.S. food chain.

"I certainly, with no hesitation, would say that every mother can feel confident that they can feed their children beef in this country," Veneman said Wednesday.

The initial outbreak was in the United Kingdom in 1986, but no cattle in the United States have ever tested positive for the disease.

Canada's first case of mad cow disease was in 1993 in a beef cow imported from Britain in 1987. Since 1990, Canada has not allowed cattle or cattle byproducts from countries with cattle that have had mad cow diseases, a Canadian agricultural department spokesman said.